Hi Brunot, it's great you got out and about with your camera. Here are some general guidelines about composition to consider. Before taking the picture ask, "What is the subject?" or "Why am I taking this photo?" The answer should be very specific and brief. Let's look at two of your examples. What is the subject of #3? I really like the look of those foreground roof tiles. But, if those are your main subject, what is all the other details about? What do the mountains and sky add? What about the antennas? IMO you have tried to include too much in this image. #4 What is the subject here? I see a lot less choices, I see interesting shapes, texture, and an animal that gives scale. What I see all fits together nicely. I see a nice contrast of color, too. The subject is easier for me to figure out. The frame does not have clutter (distractions). That small piece of railing in the lower left is one small distraction. For me a distraction is something that our eyes are drawn to, but for no important reason, so they "distract" the viewer away from what you really want us to look at.
That brings me to another composition strategy. Check the edges...top, bottom and especially the sides. Look carefully at #1. Look at the upper right edge. What is that sliver of grey doing there? Our eyes are drawn to the lightest areas of images. Do you want us looking there at that empty space? No. Look at the entire left edge. I think you should crop inwards so that we only see the front wall. That is a neat looking wall, but what about the top edge? I do not think that dark section is very interesting. It is hard to crop it all out, because the angle you used might chop off the top of the window which I think is important. I think you just tried to include a little bit too much. How about if you had just included two pigeons on either side of that neat castle relief in the wall, or maybe just a closer view of that barred window? Which leads me back to another point of composition. Do not try to include "it all" in one image. Remember, "less is more" or "if you think you are close enough, get closer".
That is why I like # 4 and #6 best. In #6 I would consider cropping out the lower dark section. We just cannot see clearly enough what is in that space. Do not distract us away from the interesting color of the walls!
#5 Cool car, but what are those people doing there> You even cut that man in half! If you were taking a picture of that car, then let us see the car. Do not let our eyes wander away to other objects that are not important.
In conclusion, I think you have a nice eye for interesting subjects, but just work a scene a little more before you shoot. What do you really want us to see. Make it as obvious as possible to have what you reacted to or what drew you to take the shot. Make the parts fit into the whole or leave them out. Look for a scene within a scene. Remember, we were not there to share the same emotions you had when you clicked the shutter, but we have all seen those images that make us say, "Wow!" That should be your goal, too! I know I could look at an old wall and go, "Wow". Can you make me do that with one of your images? Yup, but I just would have needed a little closer look.
Keep shooting and have fun!